Bushing



Feb. 6, 1940. E. E. ARNOLD 2,189,621

BUSHING Filed Jan. 13, 1938 WITNESSES:

WM 2%. 4 M

INVENTOR v Patented Feb. 6, 1940 BUB Edwin E. Arnold, Westinghouse ElHING Pittsburgh, Pa., assignor to t Manufacturing Oomh. Pa., acorporation of Application January 1:, me, w No. 184.880

.This invention relates to high-tension electrical insulating bushingsand particularly an improved construction of the shell or weather-casingthereof of the same general type as disclosed in James 5 G. I'iordscopending application, Serial No. 184,832, Med January 13, 1938, andassigned to the same assignee as this invention.

The type of bushing here involved is usually associated with anoil-immersed transformer or circuit breaker and comprises 'a dielectrictubular shell or weather easing fllled with an i ting fluid surroundingth apparatus. In order to provide a visual indication of the level ofthe insulating fluid within the bushing, a glass cylinder is mounted atone end of the weather casing to constitute an extension thereof; thenormal level of the fluid being between the ends oi the cylinder.

Gasketed joints are usually provided between e glass cylinder and theweather casing but these Joints are not entirely satisfactory in thatthey are not always leak-proof and do not result in a desired unitaryassembly. Joints which are considered to be tight become weakened undervarying temperature and stress conditions with v the result that suchJoints are apt to fail, permitting the insulating fluid to escape fromwithin the bushing or outside air to be drawn into the An object of hisinvention is the provision of a high-tension insulating bushing having asealed and leak-proof weather casing with parts substantially integrallyunited.

Another object of this invention is the pro- I vision of a bushingweather casing having thermoplastically sealed Joints between certainparts thereof.

Other objects of this invention will become apparent from the followingdescription when taken in conjunction with the accompanying drawing, thesingle figure of which is a view in elevation and partly in section ofstructed in accords tion.

Referring to the drawing, the electrical apparatus with which thebushing is to be associated includes a tubular conductor III which iswrapped with alternate layers of conducting and insulating material toconstitute a condenser type of insulator II. The lower portion 01 thecondenser bushing i2 and the tank of the immersed apparatus with whichthe bushing is to be employed are not illustrated since they are ofusual construction common in this art.

a The exposed end of the conductor and connce with the present inveneconducting lead from such a portion of a bushing condenser wrapping I!are enclosed by a dielectric tubular member or. weather casing ll ofsuitable material, such as porcelain, disposed in spaced relation'to theconductor. The casing it is provided with a plurality of radial creepageflanges it as is usual practice. I Since the space between the conductorand the weather casing is to be fllled with an insulating fluid, acylindrical shell II is so proportioned with respect to the upper end ofthe weather casing that it seats thereon when disposed in spacedrelation to the conductor. In order that the height of the insulatingliquid within thebushing may be readily ascertained, the cylindricalshell II is made of a transparent material such as glass, and is of ashape suitable for seating on the end of the dielectric weather casingin alignment therewith.

In order to maintal n the insulating liquid within the bushing and toprevent admission of air thereto, it is necessary to so seal the jointbetween the glass cylinder II and the dielectric weather casing it thatit is unatl'ected by the stresses encountered in operation, or thestresses due to the relatively diiierent expansion characand theporcelain. It has been found that a seal embodying a thermoplastic bondis entirely satisfactory in this type of service.

In making the seal a gasket 20 of a suitable thermoplastic material,such as the cellulosic materials, cellulose nitrate, cellulose acetateor cellulose acetobutyrate, is disposed between the ends of thedielectric tube and the glass cylinder. In order to promote adhesion inthe surfaces of the gasket and secure a good seal between the members ofthe weather casing, the surfaces of the gasket and, where desired, theends oi the porcelain tube and glass cylinder are coated with athermoplastic bonding material or cement which contains a suitablesolvent or plasticizer. In the making of the seal, when the bondingmaterial, usually in the liquid form, is applied to the members of thebushing and/or surfaces 01 the gasket, it is air dried either with orwithout the application oi heat to render it tacky to prevent flow inthe process of assembling the members.

With the gasket and/or surfaces thus coated, the glass cylinder andporcelain tube with the gasket therebetween are securely clampedtogether under a suitable pressure, such as 200 to 750 lbs. per squareinch and subjected to a temperature of the order of to C. fora'sufflcient length of time to cause a chemical and physical change insurface of the cell the bond and the softened ulosic material to eiiecta ll cylinder,

' taining the joint between the glass cylinder and pressures is neglibleand permanent tight junction. The assembled glass to room temperaturewhile mainand Upon examinalowed to cool porcelain tube under pressure.

tion it is found that the juncture thus formed is hard, bonding theglass and porcelain tube into an integral, leak-proof structure which iscapable of withstanding operating, temperatures and stresses encounteredin service.

In making the seal it is found that the plasticity of the thermoplasticmaterial is increased with both a rise in temperature and theapplicauntil the gasket reaches the hereinbefore described varies withthe type of thin,;stable, wafer-likeform. If the temperature of thetreatment is increased over the initial treating temperature, plasticflow again occurs reaches a stable thickness somewhat less than theoriginal thickness of, the

until the gasket gasket.

Advantage enon of the thermoplastic materials a bushing which may besubjected in service to temperatures, up to to 0., the sealis formed attemperaturesabove these values and is thus rendered stable at thetemperatures en'- countered in service. The point of stability of theseseals is affected by the temperature and pressure at which they areformed and .the initial cross-section of the area of the gasket. Thesefactors bear a definite relationship for a given material, but of coursethe relationship I material;

*{I he glass cylinder and porcelain weather casing have differentexpansion and contraction characteristics. By sealing the glass anddielectric tube with a suitable thermoplastic material, stresses set upin the seal under operating condi-- tions of the bushing or by reason ofthe unequal expansion or contraction of the members are dissipated inthe seal of the plastic material. This is because the seal is of amaterial which has a modulus of elasticity so much lower than the glasscylinder and porcelain tube that it may yield within its workable limitsto dissipate the stresses.

After the glass cylinder and weather casing are integrally united by thethermoplastic seal, the integral structure is disposed in spaced rela-'tion about the conductor and condenser bushing l2. In order to maintainthe sealed weather casing in position with respect to the conductor andto provide an expansion chamber, a hollow chamber 22 is disposed aboutthe end of the conductor and secured thereto for seating on the end ofthe glass cylinder. A gasket 24 of any suitable materials, for example,a gasket compounded from cork and synthetic rubber, is disposed betweenthe end of the glass cylinder and the bottom of the hollow chamber foreffecting a sealed joint there between.

In practice, the hollow chamber may be of any suitable form somaintained in position about the conductor as to apply a compressiveforce to the gasket between the glass cylinder and the ho]- low chamber,and maintain the glass cylinder, thermoplastic seal, and weather casingunder is taken of the stabilizing phenomgasket and'porcelain tube arethen 9.1-

in that forcompression. A hollow chamber sealingcap of this type isillustrated in issued April 2'7, 1937, to G. 'A. ternately, the type ofcap may closed. in copending application Serial No. 168,216, filedOctober 9, 1937, by Lingal and Arnold.

Bushings embodying this invention are satis- Burr et 0.1. or, al-

factory under all operating conditions encountered in practice; Underabnormal mechanical and thermal shock tests the thermoplastic seal hasbeen found to be stronger than the glass cylinder and the porcelainweather casing; the seal remaining intact under tests in which the glasscylinder and the porcelain failed.

I Although this invention has been described with reference to aparticular embodiment thereof, it is of course 'not to be limitedthereto except insofar as is necessitated by the prior art and the scopeof the appended claims.

I claim as my invention:

1. A bushing comprising, in combination, a conductor, a tubular memberof dielectric ma terial disposed around the conductor substantiallyconcentric therewith and in spaced relation'thereto, a cylinder oftransparent dielectric material having a coefficient of expansiondifferent from that of the tubular member disposed in end to endrelation therewith and in spaced relation about the conductor, athermoplastic cellulosic material disposed betweenthe confronting endsof the tubular member and the cylinder and intimately unitedtherewith,means associated with the end of the cylinder opposite its united endand the conductor for closing the space therebetween, and meansassociated with the end of the tubular member opposite its united endand the conductor for closing the space therebetween, the thermoplasticcellulosic material cooperating with the cylinder and the tubular memberto provide a leak-proof structure about the conductor;

2. A bushing comprising, in combination, a conductor, a tubular memberof dielectric material disposed aroundthe conductor substantiallyconcentric therewith and in spaced relation thereto, a glass cylinderhaving a coefllcient of expansion different from that of the tubularmember disposed in end to end relation therewith and in spaced relationabout the conductor, a gasket of thermoplastic cellulosic materialdisposed between the confronting ends of the glass cylinder and thetubular member, a binder material associated with the surfaces of thegasket whereby the glass cylinder, gasket and tubular members are flrmlyand intimately united, means associated with the end of the glasscylinder opposite 'itsunited end and the conductor for closing the spacetherebetween, and means associated with the end of the tubular memberopposite its united end and the conductor for closing the spacetherebetween, the binder and gasket cooperating with the glass cylinder'andthe tubular member to provide a leak-proof structure about theconductor.

3. A bushing comprising, in combination, a conductor; a tubular memberof dielectric material disposed around the conductor substantiallyconcentric therewith and in spaced relation thereto, a glass cylinderhaving a coefficient of expansion different from that of the tubularmember disposed in end to end relation therewith and in spaced relationabout the conductor, a seal oi cellulosic material disposed between theadjacent ends of the glass cylinder and the tubular member uniting theminto an integral structure, the cellulosic material comprising cellulosenitrate, means associated with the unsealed end of the glass cylinderand the conductor for closing the Patent No. 2,078,219,

take the form disspace therebetween, and means associated with theunsealed end of the tubular member and the conductor for closing thespace therebetween, the seal of cellulosic material cooperating with theglass cylinder and the tubular member to provide a leak-proof structureabout the conductor.

4. A bushing comprising, in combination, a conduotor, a tubular memberof dielectric material disposed around the conductor substantiallyconcentric therewith and in spaced relation thereto, a glass cylinderhaving a coeillcient of expansion different from that or the tubularmember disposed in end to end relation therewith and in spaced relationabout the conductor, a seal of cellulosic material disposed between theadjacent ends of the glass cylinder and the tubular member uniting theminto an integral structure. the cellulosic material comprising celluloseacetate, means associated with the end 01 the glass cylinder oppositeits sealed end and the conductor tor closing the space therebetween, andmeans associated with the end oi the tubular member opposite its sealedend tor closing the space therebetween,

the seal of cellulosic material cooperating with 25 the glass cylinderand the tubular member to the conductor, a seal 01' provide a leak-proofstructure about the conductor.

5. A bushing comprising, in combination, a conduotor, a tubular member01' dielectric material disposed around the conductor substantiallyconcentric therewith and in spaced relation thereto, a cylinder oftransparent dielectric material having a comcient of expansiondiii'erent from that of the tubular member disposed in end to endrelation therewith and in spaced relation about thermoplastic materialcomprising a gasket oi cellulosic material disposed between the adjacentends oi the tubular member and the cylinder uniting them into anintegral structure, a cap secured to the conductor and bearing upon theunsealed end of the cylinder for maintaining the integrally unitedcylinder and tubular member under compression and closing the spacebetween the cylinder and the conductor, and means associated with theunsealed end of the tubular member and the conductor for clodng thespace therebetween, the seal cooperating with the cylinder and tubularmember to provide a leak-proof structure about the conductor.

E. ARNOLD.

